This project is designed to determine whether the neonate is at greater risk than the adult from ingestion of certain potentially toxic heavy metals because of more rapid and/or extensive absorption from the gastrointestinal tract. In initial studies the absorption of radiolabelled mercuric chloride from in vivo closed segments of the small intestine has been found to be significantly greater in neonatal rats as compared to newly weaned or mature animals. Despite limited systemic absorption, substantial retention of mercuric ion was observed in mucosal tissue. In further studies, the significance of binding to mucosal cell proteins such as metallothionein will be determined in relation to age-related differences in absorption of mercury, as well as cadmium.